[vox-tech] Kernel not seeing all my RAM

[Cam Ellison]

Bill Broadley wrote:
> Cam Ellison wrote:
>   
>> Chanoch (Ken) Bloom wrote:
>>     
>>> I'm upgrading an x86 machine to 4 GB of RAM, and have compiled the
>>> kernel with CONFIG_HIGHMEM64G=y, but the kernel is only seeing 3283 MB
>>> of the RAM. Any idea what I'm doing wrong?
>>>
>>>   
>>>       
>> You should use the 4GB setting, I think.  The 64G setting is for a 
>> 64-bit processor, and you appear to have a 32-bit.
>>     
>
> Actually, I believe not.  The whole number of bits thing is rather confusing.
>  Is it the memory bus width?  Size of floating point?  Ints?
> Pointers/directly addressable ram?  Maximum addressable memory (ram)?
>
> Actually the "32-bit" intels (back at least to the P Pro) can address around
> 36 bits of memory via a hack, but only 4GB per process.  But the kernel could
> have 4GB and any single process could have 4GB, so on a large 32-bit server
> might have 16GB ram and allow for numerous processes to run as long as the
> total does go over 16, and any single process doesn't go over 1GB.  The config
> description should for CONFIG_HIHMEM64G should mention PAE or similar.
>
> Oh, as for the questions above:
> * it's not the memory width, 64-128 bits has been quite common for CPU
>   generations, currently it's often 192-256, and in a few weeks 384.
> * Floating point has been 64 bits for CPU generations
> * Ints aren't a bad approximation
> * Pointers aren't a bad approximation
> * addressable memory isn't
Well, as I go back and read what it actually says in xconfig, it's for a 
32-bit processor with more than 4G of RAM:

64GB (HIGHMEM64G)

Select this if you have a 32-bit processor and more than 4
gigabytes of physical RAM.

The 4GB setting is thus, and I think that's what he needs if he has a 
32-bit processor:

4GB (HIGHMEM4G)

Select this if you have a 32-bit processor and between 1 and 4
gigabytes of physical RAM.

As to my comments about 64-bit processors, I stand corrected.  And thank 
you, Bill, for the additional information.

I'm not going to quote what it says under "off" - it's too long - but 
maybe he should read that and see if he can't find the answer.  My 
interpretation is that it should be Off for a "64-bit processor".

HTH

Cam